The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams, such as slab urethane foams, are usually made by the reaction of a polyhydric alcohol with an alkylene oxide, usually ethylene oxide and/or propylene oxide, to a molecular weight of about 2,000 to 5,000 and above. These polyols are then reacted with polyisocyanate in the presence of water or other blowing agents such as fluorocarbons to obtain polyurethane foams. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane, for example, by using a polymer polyol as the polyol component. Conventional polyols may be used as the dispersing media or base polyol in these polymer polyols.
For example, dispersions of polymers of vinyl compounds such as styrene, acrylonitrile or a mixture of the two (abbreviated as SAN monomers), or of polyurea polymers, such as those prepared from toluene diisocyanate (TDI) and hydrazine in conventional polyols have been included to improve the properties of the polyols, and thus, the properties of the resulting foam. Polyurethane foams with higher load bearing properties (ILD-indentation load deflection, and CFD-compression force deflection) may be produced in this manner. It would be desirable if polymer polyols could be prepared which would be stable and have low viscosities. Stability is important to the storage life of the polyols before they are used to make the polyurethane foams. Low viscosities and small particle sizes are important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
It would further be desirable if sytrene/acrylonitrile polymer polyols could be synthesized which would have large SAN ratios. The substitution of styrene for acrylonitrile in these polymer polyols helps prevent discoloration during the cure of the polyurethane, and also helps improve flame retardability of the resultant foams. However, the stability of the polymer polyols decreases with increasing styrene to acrylonitrile ratios. That is, the components tend to separate upon standing during storage. Viscosity and particle size are also typically adversely affected with high styrene contents.
U.S. Pat. Nos. 4,539,378 and 4,539,339 describe polymer polyols made using epoxy resin-modified polyols and polyurethane foams prepared therefrom. The improvement claimed in these patents is that polymer polyols made in these epoxy resin-modified polyols as base polyols give flexible polyurethane foams with greater load bearing properties than if made with other polyols. The use of the base epoxy resin-modified polyol in polyurethane foams to give foams with enhanced properties was known at this time by virtue of U.S. Pat. No. 4,316,991. Although it is claimed therein that the monomer component is a mixture of styrene and acrylonitrile in a mole ratio of 9:1 to 1:9, equivalent to a weight ratio of about 18:1 to 1:18, all examples given therein are at styrene/acrylonitrile ratios of 40/60. In prefacing the examples therein with a general conditions statement, it is asserted that to obtain the vinyl polymer polyols of the invention that all of the epoxy resin modified polyol is preferably added first to the reaction vessel. This teaching is consistent with the examples therein.
It is well known in the art that high styrene content polymer polyols are desirable, but difficult to prepare for the reasons stated above. Regardless of the teachings of the patents discussed above, it would be unexpected to find that epoxy resin-modified polyols may be useful in preparing polymer polyols that did not only have high styrene contents, but which also had good stability, small particle sizes, and low viscosity.